1. Field of the Invention
The present invention relates to an ink jet type recording head in which a portion of the pressure chamber communicating with the nozzle opening from which ink drops are jetted is composed of a vibrating plate, and a piezoelectric layer is formed on this vibrating plate and ink drops are jetted by the displacement of this piezoelectric layer.
2. Description of the Prior Art
There is provided an ink jet type recording head in which a portion of the pressure chamber communicating with the nozzle opening from which ink drops are jetted is composed of a vibrating plate, and this vibrating plate is deformed by the piezoelectric vibrator so that ink can be pressurized and ink drops are jetted from the nozzle opening. Concerning the ink jet type recording head described above, the following two types of ink jet recording heads are put into practical use. One is an ink jet type recording head in which a piezoelectric vibrator of the longitudinal vibration mode is used, which is extended and contracted in the axial direction of the piezoelectric vibrator. The other is an ink jet type recording head in which a piezoelectric vibrator of the deflecting vibration mode is used.
The former ink jet type recording head is advantageous in that a volume of the pressure generating chamber can be changed when an end surface of the piezoelectric vibrator comes into contact with the vibrating plate. Therefore, it is possible to manufacture an ink jet recording head suitable for printing at high speed. On the other hand, the following problems may be encountered in the above ink jet type recording head. In order to manufacture the above ink jet type recording head, it is necessary to perform a difficult manufacturing process in which the piezoelectric vibrator is cut into a comb-shape while the cut portions of the piezoelectric vibrator are made to coincide with arrangement pitches of the nozzle openings. Further, it is necessary to provide a difficult manufacturing process in which the thus cut piezoelectric vibrator is accurately positioned and fixed in the pressure generating chamber. As described above, the manufacturing process becomes complicated.
On the other hand, the latter ink jet type recording head is advantageous in that, for example, as shown in Japanese Unexamined Patent Publication No. 6-40030, a green sheet made of piezoelectric material is made to adhere onto the pressure generating chamber and fired at high temperature, which is a relatively simple process, to attach the piezoelectric vibrator onto the vibration plate. However, the following problems may be encountered in the above ink jet type recording head. Since deflecting vibration is used in the above ink jet type recording head, it is necessary to provide a relatively large area to arrange the above piezoelectric vibrator. Accordingly, it is difficult to arrange the piezoelectric vibrators at a high arrangement density.
On the other hand, as shown in Japanese Unexamined Patent Publication No. 5-286131, in order to solve the above problems caused in the latter ink jet type recording head, the following arrangement of the piezoelectric vibrators is proposed. A piezoelectric material layer is uniformly formed on the overall surface of the vibrating plate by means of film forming technique. This piezoelectric material layer is cut into a shape corresponding to the shape of the pressure generating chamber by the method of lithography, and the piezoelectric vibrator is independently formed in each pressure chamber.
When the above proposal is adopted, it is unnecessary to make the piezoelectric vibrator adhere onto the vibrating plate, and the piezoelectric vibrator can be made by a simple and precise method such as a method of lithography. Further, the above method is advantageous in that the thickness of the piezoelectric vibrator can be reduced, and it becomes possible to drive the ink jet type recording head at high speed.
In the above case, while the piezoelectric material layer is provided on the overall surface of the vibrating plate, when only an upper electrode is provided in each pressure generating chamber, the piezoelectric vibrator corresponding to each pressure generating chamber can be driven. However, when consideration is given to a displacement per unit driving voltage, and also when consideration is given to an intensity of stress impressed upon the piezoelectric layer in a portion opposed to the pressure generating chamber and a portion connected to the outside, it is preferable that the piezoelectric active section composed of the piezoelectric layer and the upper electrode is arranged so that it can not protrude from the pressure generating chamber. In the ink jet type recording head in which the above deflecting mode piezoelectric vibrator is used, the piezoelectric vibrator corresponding to each pressure generating chamber is covered with an insulating layer. On this insulating layer, there is respectively formed a window (referred to as a contact hole, hereinafter) for forming a connecting section with a lead electrode which supplies a voltage to drive each piezoelectric vibrator, and this window is arranged corresponding to each pressure generating chamber. The connecting section to connect each piezoelectric vibrator with the lead electrode is formed in the contact hole.
However, the ink jet type recording head in which the above piezoelectric vibrator of the deflecting mode is used is disadvantageous in that cracks tend to occur on the piezoelectric layer in a portion where the piezoelectric active section crosses a boundary between the pressure generating chamber and the circumferential wall. Further, when the contact hole is formed, cracks tend to occur in its periphery, so that the displacement is decreased. On the other hand, there is proposed a structure in which the piezoelectric vibrator is extended from one end portion of the pressure generating chamber onto the circumferential wall.
However, in the above structure, cracks tend to occur in a portion where the piezoelectric vibrator strides a boundary between the pressure generating chamber and the circumferential wall.
In the above ink jet type recording head, in order to enhance the displacement efficiency of the vibrating plate driven by the piezoelectric vibrator, there is proposed a structure in which thicknesses of the portions of the vibrating plate corresponding to both sides of the piezoelectric vibrator are reduced. However, according to the above structure by which the displacement can be increased, the occurrence of cracks is facilitated in a portion close to the circumferential wall of the pressure chamber as described above.
The above problems tend to occur especially when the piezoelectric material layer is formed by means of a film forming technique. The reason is that the piezoelectric material layer formed by means of a film forming technique is very thin and a high intensity of residual stress exists on the material layer, so that the rigidity and the mechanical strength are lower than those of the piezoelectric layer composed of the piezoelectric vibrator that is made to adhere to the pressure generating chamber.
The present invention has been achieved in view of the above circumstances.